This is the 20th year of this training grant for post-doctoral research training focused on MD, PhD and MD/PhD scientists. The training centers on the Department of Pathology and Immunology at Washington University. We have a faculty of sixteen distributed among five departments, but having a high representation in Pathology and Immunology. The faculty is made up of a highly collegial group of immunologists and cell/molecular biologists who have interacted heavily for several years. The research of much of the faculty is on various aspects of immunology and host resistance, but also includes a heavy emphasis on the molecular basis of cell activation (for example among several, are projects on the host response to tumors and to herpes viruses, lymphocyte differentiation and activation, cell biology and biochemistry of antigen processing, the molecular basis and analysis of cell interaction molecules, regulation of DMA cycle). There are two sets of trainees. Trainees are either MDs or MD/PhDs who want to have a serious and in-depth experience in research following their clinical training in Pathology. Or fellows with a graduate degree or an MD, not associated with Pathology clinical training, having an interest in the research done by any of the faculty members: we have an applicant pool of about 100 qualified individuals, with a total of 68 postdoctoral fellows among the sixteen laboratories. Of these, ten are supported by this training grant. We request renewal of our ten training positions. A Steering Committee of five senior faculty members oversees the training and is responsible for the selection of trainees. Training includes a 2-3 year period of full-time research experience in the laboratory, where the trainee is exposed to the latest approaches in cell and molecular biology (transgenic and knockout facilities, peptide chemistry, DNA technology). Part of the training includes laboratory meetings and reports, participation in weekly seminars, and opportunities for courses in Cancer Biology. Of 48 trainees that have been supported by this Program in the last 10 years, 90% continue in research. Forty eight percent of our trainees supported during the last 10 year period are still in training while 52% have completed the program. Of the latter, 80% hold faculty positions, mostly in Pathology. This successful training program is thus producing the next generation of basic and clinician scientists who will elucidate many of the heretofore unknown mechanisms that lead to cancer development and/or discover novel therapeutic strategies that can be used to treat neoplastic disease.